1. Field of the Invention
The present invention relates to noise reduction, especially to common mode noise reduction.
2. Description of Related Art
In view of that an unshielded twisted pair cable for Ethernet transmission is subject to common mode noise and the consequent electromagnetic interference (EMI), a common mode choke is widely used for EMI reduction. A general Ethernet integrated circuit is coupled to a cable connector through a transformer, and a known art for EMI reduction is to set a common mode choke on each pair of wires between the said integrated circuit and transformer, set a common mode choke on each pair of wires between the transformer and the said cable connector, or set a common mode choke on each pair of wires at the both sides of the transformer. However, this kind of solution cannot achieve optimal EMI reduction and/or takes a lot of circuit area and cost. Therefore, the industry field looks forward to a better option.
People who are interested in the known arts may refer to the following documents:    (1) the document of U.S. Pat. No. 8,050,399; and    (2) the document of US Pat. Pub. No. 2015/0200644 A1.